A wide range of implantable medical devices are provided for surgical implantation into humans or animals. One common example is the cardiac pacemaker. Another is the implantable cardioverter defibrillator. Other examples include devices for stimulating or sensing portions of the brain, spinal cord, muscles, bones, nerves, glands or other body organs or tissues.
Implantable medical devices, particularly pacemakers, are often configured to be used in conjunction with an external programmer device which allows a physician to program the operation of the pacemaker to, for example, control the specific parameter by which the pacemaker detects arrhythmia conditions and responds thereto. For instance, the external programmer may allow the physician to specify the sensitivity with which the pacemaker senses electrical signals within the heart and to further specify the amount of electrical energy to be employed for pacing the heart in circumstances where expected heart signals are not sensed. Additionally, the external programmer may be configured to receive and display a wide variety of diagnostic information detected by the pacemaker, such as the electrical heart signals sensed by the pacemaker and the responsive pacing signals.
With regards to the display of diagnostic information, many pacemakers operate only in real time to detect electrical activity in the heart as it occurs and to transmit data pertinent thereto to the external programmer for immediately display. In other words, no capability is provided within the pacemaker for storing sensed signals for later transmission to the external programmer. Hence, diagnostic information can only be retrieved and displayed for signals senses by the pacemaker while the external programmer is currently communicating with the pacemaker, which is typically only while the patient in which the pacemaker is implanted is in a hospital or within a physician's office. With such systems, only very limited information, if any, can be stored by the pacemaker for subsequent transmission to the external programmer.
U.S. Pat. No. 5,431,691 to Snell et al. entitled "Method and System for Recording and Displaying a Sequential Series of Pacing Events", however, provides a system employing a pacemaker and an external programmer wherein the pacemaker continuously records diagnostic data pertaining to the condition of the heart of the patient for subsequent transmission to the external programmer. The data is stored within circular buffers within the pacemaker configured to ensure that, if the buffers become full, newly recorded data overwrites the oldest previously recorded data. The recorded data is ultimately transmitted to the external programmer which is configured to provide a wide variety of different displays of the data to assist the physician in analyzing the condition of the heart and rendering appropriate diagnoses. Hence a significant improvement is achieved over previous systems that were not capable of storing diagnostic data for subsequent processing and display but were instead only capable of displaying information pertaining to the current condition of the heart. U.S. Pat. No. 5,431,691 to Snell et al. is incorporated by reference herein.
The system of Snell et al. processes and records the diagnostic data in an "event record" format which allows the data to be efficiently stored, accessed and displayed. Specific types of diagnostic data processed by the system of Snell et al. are listed in TABLE I.
TABLE I EVENT NAME EVENT TYPE AV A-pulse followed by a V-pulse AR A-pulse followed by an R-wave PVE Premature ventricular event PV P-wave followed by a V-pulse PR P-wave followed by an R-wave P@MTR-V P-wave at maximum tracking rate followed by a V-pulse P@MTR-R P-wave at maximum tracking rate followed by a R-wave MAGNET Magnet placed over the implanted device--either singly or in combination with an external telemetry system
As can be seen from TABLE I, the events processed by the system of the Snell et al. patent are primarily events sensed within the heart of the patient. Event records containing information pertaining to those events are recorded within the pacemaker for subsequent transmission to the external programmer for display thereon in a variety of formats including event record displays, event bar graphs, rate bar graphs, rate time graphs, and event time graphs, each under the control of the physician operating the external programmer. More specifically, the event record display presents the various detected events of TABLE I and the corresponding pacing rate with respect to the time of the occurrence of the event. For periods of time while then pacemaker is in a dual-chamber mode (such as DDD, DDI etc.), the events presented include PV, PR, AV (or V when the mode is VDDR or VDD), AR and PVC (premature ventricular contraction). For periods of time while the pacemaker is in a single-chamber mode (such as VVI, AAI etc.), the events are presented merely as paced or sensed. The event bar graph presents a histogram of different event type for a selected period of time. The event time graph presents histograms of event types vs. time of event occurrence. The rate bar graph presents histograms of sensed and paced events vs. their rate. The rate time graph presents histograms of rates vs. times. Further information regarding the different displays may be found in the Snell et al. patent.
As can be appreciated a wide range of useful information, particularly directed to events sensed within the heart, is thereby provided to assist the physician in rendering a diagnosis as to any arrhythmia or other condition the patient may exhibit or to assist the physician in making choices as to adjusting various parameters by which the pacemaker monitors and paces the heart. The information is displayed in a variety of convenient graphical formats to help the physician visualize the information quickly and easily to facilitate prompt and accurate diagnoses.
Although the system of the Snell et al. patent represents a significant improvement over previous systems, room for further improvement remains. In particular, it would be desirable to provide a system capable of recording and displaying further diagnostic data pertaining to events in addition to those which are listed in TABLE I including, for example, diagnostic data pertaining to: events detected within the heart during refractory periods following stimulation pulses; operational events triggered within the pacemaker as a result of the condition of the patient (such as an automode switching event); and operational events triggered within the pacemaker as a result of the condition of the pacemaker itself (such as battery tests or lead fault detection tests). It is to these ends that aspects of the invention are primarily directed.